The prior art, German OS 25 43 805 discloses an injection valve wherein an improvement in the discharged fuel jet is obtained by providing spin-producing grooves above the valve seat. These grooves cause the fuel to be spun before it flows through the valve seat. A tangential force component is imparted by these spin grooves to the fuel leaving the ejection opening. Accordingly, the fuel is ejected in the form of a conical spray.
In the injection valve described in German OS 25 43 805, this advantageous spin effect is only partly utilizable. The reason for this is that after leaving the spin grooves incorporated in the periphery of the valve needle the fuel flows into the region of the undercut resulting from the manufacturing process and is markedly decelerated there. As a result, part of the kinetic energy of the fuel stream is converted into other undesirable energy forms, e.g., thermal energy.
A further disadvantage of the latter injection valve just described is that, with this type of valve, metering of the fuel quantity discharged per stroke is determined by the size of the flow cross-section of the ejection opening downstream of the valve seat when the valve is open. What results from this relationship is that the unavoidable deposits which accumulate over time in the ejection opening lead to a reduction in the cross-section of this opening and can thus further result in reduced flow quantities. This phenomenon is referred to as "narrowing down" and is regarded as hazardous to injection system operation. It also occurs with other forms of metering zones when these zones are disposed downstream of the valve seat and thus exposed to the intake manifold atmosphere.
In contrast, the advantage offered by the injection valve disclosed in U.S. Pat. No. 4,651,431 is that of metering the fuel quantity to be ejected upstream of the valve seat. For this purpose, metering bores are provided in a lower guide part of the valve needle. The fuel flows via these openings with an accompanying pressure drop. However, no measures are provided to impart a spin to the fuel. A pintle is provided within the ejection opening to atomize the fuel.